Wednesday, March 16, 2016

WHO: H1N1v Cases In China

#11,153

While avian flu viruses have garnered the bulk of the media's interest over the
past few years, swine variant viruses (H1N1v, H1N2v, H3N2v) are also
consider a potential source of pandemic viruses, and in 2009 we saw
exactly that when a swine-origin H1N1 virus jumped to humans.

The subtypes of flu viruses that commonly
spread in swine (H1, H2 & H3) are also the same subtypes that have caused
all of the known human pandemics going back 130 years (seeAre Influenza Pandemic Viruses Members Of An Exclusive Club?), and are generally regarded as having less far to `jump’ to than many avian viruses.

Although human infections with swine-origin viruses are only rarely reported (only 5 in the United States in 2015),
in 2012 the United States saw more than 300 cases, possibly the result
of the acquisition of the M gene from the 2009 H1N1 virus, which may
have enhanced its transmissibility.

Surveillance is problematic, however, since few with mild to moderate flu symptoms are ever tested, even in the United States. In other countries, the odds of detecting human swine flu cases are pretty remote, although in countries monitoring for avian flu (China & Egypt mostly), the odds are a little better.

Our study shows the potential of
EAH1N1 SIVs to transmit efficiently in humans and suggests that
immediate action is
needed to prevent the efficient
transmission of EAH1N1 SIVs to humans.

Although more than half of the viruses sampled in the PNAS report fell into the EAH1N1 lineage, there are a number of other swine H1N1 variants circulating in China as well.

All of which brings us to the latest WHO Influenza at the Human-Animal Interface summary (dated Feb 25th, but only released in the past 24 hours), which includes this entry on three Chinese swine variant virus infections going back to the middle of 2015.

A 2.5-year-old male from Hunan Province with illness onset on 30 June 2015 was detected through sentinel Severe Acute Respiratory Infection (SARI) surveillance. The patient was hospitalized with pneumonia and later recovered. He had no underlying medical conditions. The case investigation found that the case was exposed to pigs in his village.

The second and third cases were a 5-year-old female and a 4-year-old female from different cities in Yunnan Province with illness onset on 17 November and 22 November 2015 respectively. The cases were detected through sentinel Influenzalike Illness (ILI) surveillance and both had mild symptoms. Exposure history for both cases is not known.To date, a total of seven laboratory-confirmed cases of human infection with this Asian sub-lineage A(H1N1)v virus have been detected in China. The haemagglutinin (HA) gene recovered from viruses detected in the most recent three cases grouped with swine influenza A(H1N1) viruses circulating in China.

Risk Assessment:1.What is the likelihood that additional human cases of infection with influenza A(H1N1)v viruses will occur?Influenza A(H1N1) viruses circulate in swine populations in many regions of the world. Depending on geographic location, the genetic characteristics of these viruses differ. Most human cases are exposed to the A(H1N1) virus through contact with infected swine or contaminated environments. Human infection tends to result in mild clinical illness. Since these viruses continue to be detected in swine populations, further human cases can be expected.

2. What is the likelihood of human-to-human transmission of influenza A(H1N1)v viruses?No case clusters have been reported. Current evidence suggests that these viruses have not acquired the ability of sustained transmission among humans, thus the likelihood is low.3. What is the risk of international spread of influenza A(H1N1)v viruses by travellers? Should infected individuals from affected areas travel internationally, their infection may be detected in another country during travel or after arrival. If this were to occur, further community level spread is considered unlikely as these viruses have not acquired the ability to transmit easily among humans.

For more on the potential of the next pandemic to emerge from pigs, you may wish to revisit: